Aspirin and other NSAIDs use in relation to incident breast cancer risk.

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The use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) is widespread for treatment of common symptoms such as headaches, muscular pain, and inflammation. In addition, the use NSAIDs in chemoprevention is increasingly more common, for diseases such as heart disease and colon cancer. Data for a protective effect of aspirin or other NSAIDs on breast cancer risk has been inconsistent. We assessed the associations of aspirin use and other NSAIDs use with the risk of breast cancer among premenopausal women in the prospective Nurses' Health Study II cohort. A total of 116,609 women, ages 26 to 42 years and free of cancer, were followed for up to 14 years. Multivariate relative risks (RRs) and 95% confidence intervals (CIs) were calculated by Cox proportional hazards models, adjusting for age and other important breast cancer risk factors. Overall, 1,345 cases of invasive breast cancer were documented during follow-up. Regular use of aspirin (2 or more times per week) was not significantly associated with breast cancer risk (RR=1.05, 95% CI (0.90-1.23)). Frequency (days per week) and dose (tablets per week) were not associated with breast cancer risk, but risk appeared to increase with longer duration of regular use (RR=0.99, 95% CI (0.83-1.18) for <5 years and RR=1.37, 95% CI (1.02-1.86) for 5 or more years of use). Regular use of non-aspirin NSAIDs was associated with an increased breast cancer risk overall (RR=1.21, 95% CI (1.05-1.39)), and was similar by duration of use (RR=1.20, 95% CI (1.04-1.39) for <5 years and RR=1.23, 95% CI (0.99-1.53) for 5 or more years of use). Frequency and dose were not associated with risk. Use of acetaminophen was not associated with breast cancer risk examining regular use, frequency, dose, or duration. These data suggest that use of aspirin and other NSAIDs is not associated with a reduced risk of breast cancer among premenopausal women, and may be associated with a modest an increased risk.